In domestic appliances which are powered by methane, propane or other domestic gases, it has been a long recognized practice to provide for the termination of flow of gas in the event that the pilot flame (pilot light) of the appliance is extinguished. As is well known, in such an event there can be excess accumulation of gases and possible explosion, either from gas issuing through the pilot flame orifice or from the main burner.
One of the principal devices in current use which achieves the foregoing objective is a gas valve having a magnetic actuator. U.S. Pat. No. 3,998,425 to Braucksiek shows a typical device of this sort. The essential operation of such devices is as follows. The sealing part of the valve, adapted to physically terminate the flow of gas from a source, is spring biased toward the closed position. Activation of an electromagnet holds the valve in the open position against the spring biasing force when it is powered by the output of a thermopile or other heat-to-electrical energy conversion device which is placed in the flame. Should the flame be extinguished and thus stop providing a source of heat, the electrical current flow from the thermopile is substantially lowered, thus causing the electromagnet to lose a substantial portion of its force; whereupon, the spring force overcomes the magnetic force and the valve closes. Generally, the valve is reset manually when the flame is rekindled.
As reference to the patent and to the subject matter of the present invention will reveal, such safety valves have a number of parts, not unlike other electromagnetic devices. And since the devices are used in great quantity in domestic appliances for which the market is very competitive, it has always been a desire to make them at a low cost. Of course, the incentive to lower the cost must be balanced against the need for absolute reliability in performing the intended function of the valve, which is to provide for the safety of persons and property.
Safety valves are physically relatively small and heretofore the multiplicity of parts comprising the valve have been manually assembled. The labor involved in assembling an actuator part of the valve is a significant part of the cost of a valve. Of course, the usual attention has been given to the design of the actuator and to tools used by assemblers, in order to lower costs as best possible.
Now, assembly robots have become available and it has been sought to apply such machines to the constuction of a magnetic actuator for a safety valve. An assembly robot is a computer guided machine which is adapted to functionally replicate the acts of human operators in putting diverse components together into a final product. The assembly operation has always been a difficult area, compared to some other areas of using robots, as those in the robotics field know well. In particular, it is presently necessary that the parts be spatially oriented in particular ways and that a variety of dexterous movements be performed. In addition, there are many visual clues received by a human assembler and at the present state of robotic art it is not possible to replicate human visual acuity and response. These limitations were particularly apparent when it was sought to apply an advanced robot (IBM System/1) to the task of assembling a magnetic actuator. For example, the prior art hand-assembled actuator was comprised of small wafer-like insulators and was partially joined together by soldering. Not only were there the problems of orientation, handling and locating of parts, but the soldering operation was inherently time-limiting, in that it required time for both heating and cooling.
When these limitations became apparent, the design and construction of the actuator had to be improved in order to facilitate automation. In doing this, other improvements were also realized as will be apparent from the remainder of this description.